This invention pertains to flexible covers for clarifiers, and more particularly, the present invention pertains to the sealing of a flexible cover over a clarifier for maintaining the content of the clarifier in a sealed environment.
A typical industrial clarification installation comprises a plurality of reservoirs or holding tanks to be filled with mill effluent. Clarification is normally effected by alternatively agitating and letting the effluent settle, and lifting floating scum from the surface of the effluent or scooping sediments at the bottom of the reservoir. These holding tanks are generally equipped with mechanical equipment that must be accessible for inspection, maintenance or for repair.
The clarification process is often accompanied by a fermenting action and a generation of odorous bio-gases, and/or the release of volatile organic carbons. For environmental reasons, these gases must be collected and treated. Therefore, a clarification reservoir, or clarifier, is preferably covered and sealed to contain the gases. Also, a clarifier preferably has a piping system to transport the gases to a gas treatment plant.
When a removable flexible cover is installed over a clarifier, the installation must resist wind forces that tend to flap portions of the cover and stretch it laterally. Also, the attachment of a flexible cover must be sufficiently strong to permit one of more workers to walk on the flexible cover to fix it if the need arises.
A clarifier having a removable flexible cover mountable thereon must also provide for a certain level of safety when the cover is removed. During maintenance activities for example, it is common to find power tools, welding machines, acetylene torch carts and maintenance wagons along the perimeter of the clarifier. It is therefore important to prevent workers and equipment from sliding into the reservoir.
Examples of various systems available for covering a reservoir are described in the following documents:
U.S. Pat. No. 3,195,310 issued on Jul. 20, 1965 to C. E. Schroeder;
U.S. Pat. No. 4,324,370 issued on Apr. 13, 1982 to W. Guard et al.;
German Patent DE 2,938,496 published on Apr. 24, 1980;
French Patent FR 2,668,195 published in Apr. 24, 1992.
Although the flexible covers of the prior art deserve undeniable merits, it is believed that these systems do not meet all the requirements for a flexible clarifier cover which is securely mountable, removable and safe. It is believed that there continues to be a need for a new removable flexible cover which may be positively sealed, which can support workers walking thereon and which provides for a safe working environment.
In the present invention, however, there is provided a removable clarifier cover which has safety features incorporated therein, which is particularly efficient for sealing a clarifier in a manner to resist wind stresses and to support workers walking thereon.
In a first aspect of the present invention, there is provided a removable cover for retaining off-gases inside a clarifier having first, second, third and fourth walls. The cover comprises a flexible sheet laid across the clarifier and having first, second, third and fourth margins. There are also provided means for retaining and sealing the first margin to the first wall, and means for pulling and releasably sealing the second, third and fourth margins to the second, third and fourth walls respectively. The means for retaining and sealing the first margin to the first wall comprise a first structural angle extending along the first wall and having a leg member aligned upwardly. The means for pulling and releasably sealing the second, third and fourth margins comprise spaced-apart pullers mounted inside second, third and fourth structural angles extending along the second, third and fourth walls respectively and each structural angle has a leg member aligned upwardly.
In this aspect of the present invention the first, second, third and fourth walls, and the flexible sheet are usable for containing off-gases inside the reservoir and the first, second, third and fourth structural angles constitute kick plates enclosing the clarifier for enhancing the safety of workers working around the clarifier.
In another aspect of the present invention, the clarifier cover comprises a plurality of spaced-apart trusses mounted across the clarifier and the flexible sheet is laid over the spaced-apart trusses. In this aspect of the invention, the flexible sheet is selectively rolled-up over the spaced-apart trusses for accessing equipment inside the reservoir.
In accordance with another aspect of the present invention, the means for pulling and releasably sealing the second, third and fourth margins against the second, third and fourth walls respectively also comprise cables affixed to the second, third and fourth margins of the flexible sheet and individually attached to a respective puller. Each of the pullers has a cable deflector bar extending substantially at a same level as a plane of mounting of the puller. These pullers are advantageous for pulling the margins of the flexible sheet against the mounting surface of each puller for facilitating the sealing of the flexible sheet against the second, third and fourth walls.
In accordance with yet another feature of the present invention, there is provided a removable cover for retaining off-gases inside a clarifier having first and second opposite side walls, and a pair of opposite end walls. A plurality of spaced-apart trusses are mounted across the first and second side walls. The trusses comprise first and second outmost trusses each having an arched plated structure attached thereto, and a series of intermediate trusses disposed between the first and second outmost trusses. The flexible sheet is laid over the spaced-apart trusses and the outmost trusses. The flexible sheet has first and second longitudinal margins and first and second transversal edges. The clarifier cover further has means for retaining and sealing the first longitudinal margin to the first side wall; means for pulling and releasably sealing the second longitudinal margin to the second side wall, and means for pulling the flexible sheet across the trusses and for releasably sealing the first and second transversal edges to the first and second outmost trusses respectively. The means for pulling and releasably sealing the second longitudinal margin against the second side wall further comprise a pipe affixed to the second longitudinal margin, a first series of pullers mounted to the second wall and a resilient pad extending under and adjacent the first series of pullers. Each puller has means for pulling the pipe and the second longitudinal margin downward against the resilient pad for sealing the second longitudinal margin against the second side wall.
The means for pulling the flexible sheet across the trusses and for releasably sealing the first and second transversal edges against the first and second outmost trusses respectively comprise grommets along the first and second transversal edges of the flexible sheet. Cables extend through the grommets. Second and third series of pullers are affixed to the first and second outmost trusses respectively. The pullers have means for pulling the cables and the first and second transversal edges against the first and second outmost trusses respectively for sealing these transversal edges against the outmost trusses.
The first, second and third series of pullers have ratchet-type mechanisms that are easily worked for selectively releasing the flexible sheet for opening the clarifier and exposing the equipment inside the clarifier.
Other advantages and novel features of the present invention will become apparent from the following detailed description.